The present invention relates to an intracranial pressure relief valve and, more particularly, to a three stage valve having adjustable valve stem members which not only adjust closing pressure but also regulate fluid flow during three stage operation of the valve.
Hydrocephalus is a condition in which the body, for any one of a variety of reasons, is unable to relieve itself of excess cerebrospinal fluid (CSF) collected in the ventricles of the brain. The excessive collection of CSF in the ventricles results in an abnormal increase in both epidural and intradural pressures. This may in turn cause a number of adverse physiological effects including compression of the brain tissue, impairment of blood flow in the brain tissue, and impairment of the brain's normal metabolism.
Treatment of a hydrocephalic condition frequently involved relieving the abnormally high intracranial pressure. To this end, a variety of CSF pressure regulator valves and methods of controlling CSF pressure have been developed which include various check valves, servo valves or combinations thereof. Generally, such valves serve to divert CSF from the ventricles of the brain through a discharge line to some suitable drainage location in the body, such as the venous system or the peritoneal cavity. The check valves operate by opening when the difference between CSF pressure and pressure in the discharge line exceeds a predetermined level.
The use of a simple check valve in the treatment of hydrocephalus is potentially disadvantageous since it is possible for such a valve to open in response to a sudden, but nevertheless perfectly normal, increase in differential pressure between CSF in the ventricular spaces and fluid at the selected discharge location of the body, resulting in abnormal and potentially dangerous hyperdrainage of the ventricular spaces. For example, when a patient stands after lying in a recumbent position, the resulting increased vertical height of the fluid column existing between the head and the selected drainage location may result in such an increase in differential pressure. Accordingly, valves, such as that described in the copending application of the present inventor, Ser. No. 672,868, filed Nov. 19, 1984, have been developed which serve to prevent undesired hyperdrainage by limiting the flow rate of fluid through the valve when a sudden increase in differential pressure occurs.
In this valve, a diaphragm is movable in response to the pressure differential between ventricular CSF pressure in an outlet chamber on one side of the diaphragm, and the pressure of fluid at the drainage location of the body in an outlet chamber on the other side of the diaphragm. The diaphragm has a valve seat which forms a fluid metering orifice. The valve stem extends through the orifice to provide fluid metering between the two chambers. The motion of the diaphragm in response to changes in differential pressure in the valve chambers cause the valve seat to move from a first position, in which the valve seat engages a section of the valve stem to provide a first valve condition in which the orifice is blocked and fluid flow is prevented within the diaphragm moves the valve seat to a second position, in response to an increased pressure differential between the two chambers a second valve condition is provided in which fluid flow between the chambers is sufficient to maintain a first substantially constant predetermined pressure in the first chamber. In response to a sudden increase in differential pressure, such as might be caused by a drastic change in the position of the patient, such as movement from a recumbent position to a vertical position, the diaphragm and valve seal move relative to the valve stem assembly to establish a third valve condition wherein flow between the chambers is controlled at a substantially constant flow rate. In order to prevent hyperdrainage, any further movement of the diaphragm and valve seat relative to the valve stem creates a fourth valve condition wherein a second substantially constant predetermined pressure in the first chamber is maintained.
A CSF pressure relief valve is typically miniaturized for implantation and is required to perform with a high degree of precision under highly demanding conditions throughout a rather extensive, ever-changing mode of operation. Consequently, it has been necessary to carefully control the dimensions of the various parts of the valve, particularly the valve seat, the valve stem assembly and the orifice defined by the valve seat. The parts involved are quite small, and working tolerances on the order of 0.0001 of an inch must be met. Considerable manufacturing costs may be incurred in constructing such a valve.
A CSF pressure relief valve incorporating a one piece valve stem is described in the copending application of the present inventor, Ser. No. 609,137, filed May 8, 1984. An alternative construction for the valve members is described in the copending application of the present inventor entitled Three Stage Intracranial Pressure Control Valve filed concurrently herewith. The present invention is directed to an improvement in the valving mechanism, particularly the valve stem assembly, and, in conjunction therewith, the valve seat and the orifice defined thereby. Basically, this improvement utilizes one or more adjustment means operative with respect to the valve stem assembly so as to permit external adjustment of certain parts thereof to not only adjust the closing pressure of the valve, but also to adjust the fluid flow response of the valve in carrying out the multiple conditions of fluid flow operation. For example, by utilization of the adjustment features of the valve of the present invention, certain tolerances can be eliminated or made less critical and, as a result, the cost of the valve can be reduced. Other advantages will become apparent from the following detail description.
In view of the foregoing, it is a general object of the present invention to provide a new and improved pressure regulator valve for relieving intracranial pressure caused by the presence of excess CSF in the ventricles of the brain.
It is a more specific object of the present invention to provide a pressure regulator valve which includes components which may be more easily and economically manufactured.
It is a still more specific object of the present invention to provide a pressure regulator valve in which there is an improved mechanically adjustable relationship between the valve stem assembly or certain parts thereof and the valve seat carried on the diaphragm and defining the fluid flow orifice.